说明：  构造哈夫曼树HT，动态分配数组存储哈夫曼树 ，-无栈非递归遍历哈夫曼树，求哈夫曼编码。
(Huffman tree structure HT, dynamic allocation of array storage Huffman tree- no stack traversal non-recursive Huffman tree, and Huffman coding.)